Trencher tooth construction

ABSTRACT

A trenching apparatus of the orbital cutter chain type including a plurality of trencher teeth mounted at spaced intervals along the length of the chain, adjacent teeth oriented outwardly at different angles. Each tooth comprises a cutting bit secured in a recess formed in and opening to one side of a polygonal holder having another side thereof secured by welding to the planar platform of a Pi shaped cross-section carrier. The carrier is adapted to be bolted removably to a chain link. The cutting bit has a concave leading edge and a convex trailing edge. The holder has an irregular peripheral ring of so-called hard surfacing metal material welded to its leading face whereby to enable both cutting bit and holder to perform a digging function and, as well, to enable the structure to move the broken material from the trench. The selection of the side joined to the carrier determines the angular orientation of the tooth relative to the chain.

United States Patent 1191 Strauss et al.

[ 1 Oct. 21, 1975 TRENCHER TOOTH CONSTRUCTION [73] Assignee: Service Dynamics, Inc., Lake Bluff,

Ill.

[22] Filed: June 25, 1973 [21] Appl. No.: 373,430

[52] US. Cl 299/84; 37/83; 37/142 R;

37/191 A; 83/831; 299/91 [51] Int. Cl. E02F 9/28 [58] Field of Search... 37/83, 191 A, 192 A, 141 R, 37/142 R1141 T, 142 A; 299/84, 92, 91, 79, 82; 83/831; 30/381-387 2,965,365 12/1960 Krekeler ..299/92 Primary ExaminerClifford D. Crowder Attorney, Agent, or FirmSi1verman & Cass, Ltd.

[ 5 7] ABSTRACT A trenching apparatus of the orbital cutter chain type including a plurality of trencher teeth mounted at spaced intervals along the length of the chain, adjacent teeth oriented outwardly at different angles. Each tooth comprises a cutting bit secured in a recess formed in and opening to one side of a polygonal holder having another side thereof secured by welding to the planar platform of a Pi shaped cross-section carrier. The carrier is adapted to be bolted removably to a chain link. The cutting bit has a concave leading edge and a convex trailing edge. The holder has an irregular peripheral ring of so-called hard surfacing metal material welded to its leading face whereby to enable both cutting bit and holder to perform a digging function and, as well, to enable the structure to move the broken material from the trench. The selection of the side joined to the carrier determines the angular orientation of the tooth relative to the chain.

16 Claims, 7 Drawing Figures US. Patent (9921,1975 sheetlofz 3,913,979

d a 9 u a Q W W m Q 9 V a, W" a E m o US. Patent Oct. 21, 1975 Sheet20f2 3,913,979

FIG. 6' FIG. 7

TRENCI-IER TOOTH CONSTRUCTION BACKGROUND OF THE INVENTION Field of the Invention ing a plurality of trencher teeth oriented outwardly at different angles relative to the direction of movement of the chain, said trenching apparatus being effective for operation upon all surface materials under variable environmental conditions to break ground and to move the broken material or spoils, leaving a clean trench.

Apparatus for the digging of trenches such as utilized for cable laying, curb preparation, pipe laying and the like purposes usually are characterized either by the use of mechanical shoveling machines either consisting of a single digging bucket or a plurality of bladed members mounted on a belt or chain. These implements are capable of breaking ground and carrying the excavated material to a repository remote from the excavation.

The size, portability, part replacement and efficiency of known trenching machinery leaves much to be desired and hence there has been a long felt need to provide a portable above ground trenching apparatus which is relatively lightweight, portable, versatile, easily fabricated and additionally, where removal and replacement of individual parts can be facilitated.

It is well known in the methodology of below ground mineral mining, to employ a multiplicity of cutting elements arranged to a cutter chain, bit ring or boring arm of a continuous mining apparatus so as to break up and remove sections of mineral from a vein thereof. The cutter bits utilized may be spaced longitudinally of an orbital path in which they are forced to travel and are advanced at substantially right angle to the orbital path so as to attack and disintegrate the material to form a kerf or channel in the mineral of substantial crosssectional area from which the mineral has been removed. It is known to secure the cutter teeth of such mining machinery permanently to the links of the chain or on carriers that are secured permanently to the chain. Where the carrier is secured permanently to such links, individual teeth have been provided which are seated removably upon holders generally utilizing bolts and like fastenings to enable the individual cutter bits or teeth to be removed and replaced after wear or fracture in the course of use. Generally, carriers for the teeth have been a part of the chain.

In contrast to underground mining operations, which treats more or less uniform material, surface trenching requires equipment capable of operating on a widely differing range of materials under considerably varied conditions. Tough, rocky soil is encountered as well as hard, frozen ground. It would be advantageous for the trenching apparatus to be as effective for sand, gravel, mud, packed dirt and combinations thereof. Capability for breaking and tearing into varied character surfaces is essential but, in addition, a clean trench should result. Accordingly, the trenching apparatus should be equally capable of versatility in moving the spoils or broken material to provide the clean trench and without an additional apparatus or operation.

So far as is presently known, there has not been available in the mining industry or the field of trenching equipment, any trenching apparatus or tooth structure having the aforedescribed versatility. One problem encountered is that of wear. Considering the type of surfaces treated, teeth presently employed are subject to rapid wear which results in increased expense, reduced useful life of the teeth, necessary and frequent replacement of worn teeth and resultant downtime cost, difficulty in removing and replacing worn or broken teeth and inability of presently available teeth and apparatus utilizing same to move the broken material out of the trench to leave a clean trench. Limitations as to depth of cut likewise have reduced the effectiveness of known trenching equipment.

The angles of orientation for the teeth are determined by utilizing means such as tightening screws or bolts to vary the angular relationship of the tooth to the holder per se. Variable orientation of the holders also is known. Known structures of the character described have been productive of a quantity of dust or other fine size portions which is difficult to remove and most often clogs the chain or packs same, as well as the individual teeth reducing their cutting effectiveness. The kerfs or narrow channels in the wall of a vein for which this type of machinery has been utilized are used to provide cavities for placing explosives of the type used to disintegrate or knock down the particular mineral wall, facilitating removal of relatively large quantities of mineral. The nature of the kerfs or channels formed utilizing cutting chain assemblies is such as to require only short duration individual cutting operations rather than the much longer continuous usage that is required in trench digging operations.

Further, the mineral material merely has to be pulverized-that is broken without requiring its removal since the explosive charges can be introduced even with a residual quantity of spoils remaining in the kerf. However, in trenching, the excavation must be clean; the broken material necessarily must be removed. Either the same machine which breaks must remove or a second removal operation is necessary. This is costly in time, labor and/or additional machinery requirements. Known machinery of the cutting chain" type used for mining operations are not suitable for moving the broken material.

One other characteristic difference between surface trench digging operations and underground mining operations is the normal substantial length of the trench required, and as mentioned earlier, the different character of the material encountered as compared with the below ground mining operation. Difficulties encountered in fabrication of the teeth as well as disassembly thereof from the chain to enable replacement should one or more of the teeth be worn or fractured during use, for example deter from the use of chain type machinery in surface or above ground trenching.

It is desirable to provide trenching apparatus, and particularly trencher teeth therefore which are versatile, effective for most ground and near surface conditions such as hard-frozen, sand, gravel, mud, rocky soil which may be encountered. The teeth should be removable easily from the orbital chain, be capable of breaking and moving the broken material to form a clear excavation and be easily fabricated.

SUMMARY OF THE INVENTION A trenching apparatus including an orbital chain carrying trencher tooth assemblies mounted thereon at spaced intervals along the length thereof, adjacent teeth oriented at a different angular position relative to the direction of travel of the chain. Each tooth assembly includes a removable steel cutting bit secured by a pin and socket arrangement removably to an otherwise solid body of polygonal cross-sectional configuration welded in place angularly on the planar platform of a Pi-shaped carrier, brace means weldably secured to the holder and to the carrier for maintaining the angular position of the holder and the legs of the carrier are secured removably to the links of the chain. The angle of orientation of the tooth is determined by the angular orientation of the holder. An irregular ringlike peripheral formation is formed on the leading face of the holder to increase the useful life of the assembly and to enable the tooth and tooth holder to function as a unit in breaking and moving the material to form a clean excavation. The said ring-like formation is of hard surfacing material weldably applied to said leading face.

DESCRIPTION OF THE DRAWING FIG. 1 is a fragmentary perspective view of a trenching apparatus constructed in accordance with the teachings of this invention and illustrating the forward portion of the orbital chain thereof and the arm supporting same.

FIG. 2 is a partially exploded perspective view of a portion of the trenching apparatus illustrated in FIG. 1.

FIG. 3 is an exploded perspective view of a tooth assembly constructed in accordance with the invention.

FIG. 4 is a front elevational view of a tooth assembly constructed in accordance with the invention as viewed mounted to one of the links of an orbital chain.

FIG. 5 is a sectional view taken along lines 55 of FIG. 4 and in the direction indicated.

FIGS. 6 and 7 are diagrammatic views illustrating the manner by which the cutter or trencher teeth can be angularly oriented in accordance with the teachings of the invention.

DESCRIPTION OF PREFERRED EMBODIMENT Briefly, the invention herein provides apparatus of the general type heretofore used in underground mining which is particularly adapted for forming trenches at surface or ground level. The trenching apparatus according to the invention utilizes a cutting chain of the orbital type normally employed in forming kerfs or channels in the course of underground mineral mining operations. Such orbital cutting chains have a plurality of cutting teeth secured at spaced intervals therealong.

According to the invention adjacent teeth are oriented at different angles relative to the direction of movement of the chain. Variation of about nine angles is preferred. The teeth are mounted on multi-sided, generally polygonal cross-section, substantially solid holders which are welded individually to carriers having a cross-sectional configuration of the greek letter Pi. The depending legs of the carrier are perforated to enable slipping of the carrier on the chain link and fastening of same to the chain link by nuts and bolts for example. A brace is welded both to the carrier and the holder for angled positions of the holder to maintain its position. The angle of orientation of the tooth is determined by the disposition of the holder on a selected one of its sides. The teeth are removable from the holder with use of a particularly configured tool. The structure according to the invention particularly is characterized by a hard surfacing metal material applied as a peripheral ring formation to the leading face of the holder. The ring formation is somewhat irregular in topography. and defines a somewhat cup shaped leading face whereby to enable the tooth and holder to function as a unit in not only breaking but also moving the broken material from the excavation to leave a clean trench.

Referring now to the drawing, the forward end of the trenching apparatus constructed in accordance with the invention is illustrated in FIG. 1, and generally is designated by reference character 10. The trenching apparatus 10 includesan elongate scraper arm 12 having a scraper member 14 secured at arcuate terminal end 16. An orbital endless link chain 18 carries a plu rality of tooth assemblies 20 mounted thereon at spaced intervals therealong. The chain 18 is supported on sprocket wheels 22 mounted for free rotation on shafts 24 journaled on bracket pairs 26, which respectively are secured on opposite sides of arm 28. Arm 28 is of hollow construction and has a rectangular crosssectional configuration. A member 30 of conforming rectangular configuration is engaged telescopically within the open end 32 of tube 28. Member 30 terminates in a mounting 34 carrying wheel 36.A rigid bar 38 is connected to the forward end of arm 28 by,

bracket 40 and to mounting 34 by bracket 42. This arrangement permits adjustment of tension on the chain 18. The trenching apparatus 10 is mounted on a vehicle (not shown) or the like so that it is capable of being propelled with the chain moved along its orbital path' as a result of the teeth thereof encountering the ground surface.

The trencher tooth assemblies 20 according to the invention are mounted on the links 44 of the chain 18.

Each of the links 44 comprises a pair of spaced plate members 46 and 46' having aligned passageways 48. The plates 46 and 46' are secured to the bridging links 50 by means of bolts 52. The trencher tooth assembly' 20 comprises a tooth 54 having a leading generally concave portion 56 and a trailing generally convex portion 58, a depending tapered shank 60 and a tip in the form of an insert of very hard material such as carbide. seated at the upper leading portion 57' of the tooth 54. The tooth 54 has a peripheral bottom flange 62 and immediately above said flange 62, a pair of lugs or upsets 64 and 64 is formed. Lugs 64and 64 extend outwardly in respective opposite directions in a horizontal plane normal to the tooth 54.

A tapered shank 60 depends from the base of tooth 54 and has a rounded leading face 66 and a trailing portion 68; the opposite long sides 70 of shank 60 lie in somewhat parallel planes. The shank 60 has an arcuate notch 72 formed therein opening to the trailing portion 68 thereof. The notch 72 is concave and has rounded corners 74 at its mouth.

The width of shank 60 is substantially the same as the width of the tooth 54, but the leading to trailing edge dimension of the shank at its greatest value is less than the leading to trailing edge dimension of the tooth along the flange 62. Thus, the shank is set back sub-. stantially from the trailing end 58 of the tooth and is set back from the leading and side edges of the flange 62.

A holder 76, preferably formed of a short length of steel or the like is adapted to receive the tooth 54 secured herein. The holder 76 is formed of a substantially solid bar of octagonal configuration having leading and -trailing faces or ends 78, 80 respectively, four narrow flat sides 82 and four wider flat sides 84 alternating with and spaced one from the other about the circumference of holder 76 by the narrow flat sides 82. A slot 90 is formed in the holder 76 opening to at least one side 84, of the holder. The slot 90 is of sufficient size and configuration loosely to receive the full length of shank 60 therein.

According to the invention, the holder 76 may be described as being of generally polygonal cross-section, multi-sided or multi-faceted, with at least the leading face surface being generally in a plane normal to the axis of holder 76.

A transverse passageway 92 is formed in the holder 76 opening to opposite wall 84 and at right angle to the slot 90. The transverse passageway 92 is located to intersect a portion of the slot 90. A cylindrical plug 94 having a bevelled end 96 is formed preferably of plastic material such as nylon, for example. The diameter of plug 94 is only slightly less than the diameter of transverse passage 92 to enable the plug 94 to be press-fitted into transverse passage 92 while the shank 60 of tooth 54 is seated in slot 90. The notch 72 is located on the shank 60 so that on seating of the flange 62 fully in slot 90 of holder body 76, the notch 72 is aligned with the transverse passage 92. Accordingly, when the plug 94 is press-fitted through the transverse passage 92, it passes through the notch 72 and hence the tooth 54 is locked in position. The length of plug 94 is selected so that only the bevelled end 96 protrudes from wall 84.

An irregular ring-like formation 86 is applied to the leading face 78 of the holder 76. Formation 86 is formed of hard-surfacing material such as sold under the trade designation Raynite Rod BXC OT 4410. Formation 86 is applied to the leading face 78 by a welding process.

Accordingly, formation 86 with leading face 78 of the holder, defines an overall cup-like configuration, cooperating with the leading face 66 of tooth 54 to function as a unit, not only to break and tear the surface against which it impacts but, as well, moves the material to provide a clean excavation or trench.

The holder 76 is arranged on the planar surface 102 of carrier 100 so that the sides 84 and 86 are parallel to the long edges 104 of the carrier. The carrier 100 has a cross-sectional configuration of the Greek letter Pi defined by a planar platform 106 and a pair of depending legs 108 and 110. The legs 108 and 110 are spaced apart following planes parallel one to the other and parallel to the long edges 104 of the platform 106. Legs 108 and 110 are located respectively inwardly of said edges. A pair of spaced openings 112 is formed in each of the legs. Openings 112 carried by leg 108 are aligned with opposite openings 112 carried by leg 110.

The platform 106 preferably is formed of metal capable of having the holder 76 welded thereto. As is evident from the illustration, when tooth 54 is installed in slot 90 of holder 76, it extends outward from the holder 76 at a 90 angle relative to the plane defined by a side 84 of the holder. Since sides 84 are parallel, the angle of orientation of the tooth relative to the direction of movement of the chain 54 is determined by angular positioning of the holder 76 on the top planar surface 102 of platform 106 in a direction substantially parallel to the opposite elongate edges 106 thereof. The holder 76 may be secured to the platform surface 102 resting on one of its narrow sides 82 so that the tooth will project at an angle of orientation relative to the direction of travel of the chain of approximately 45. Angular disposition at the juncture of sides 82 and 84 offers another angular position for tooth 54. The weldment 114 can be provided in sufficient quantity to define a pillow so as to enable adjustment of the disposition of the holder whereby approximately any selected angle of orientation can be effected for the tooth 54. This is illustrated in FIGS. 6 and 7.

Most often there are four different angular dispositions on one side of the platform and a like four directed toward the opposite side of the platform, plus a straight up orientation of tooth 54making a total of nine. More than one holder and tooth can be placed on one platform and the platforms may be of different width. In this way, just about any desired width trenches can be formed simply by a selection of trencher tooth assemblies.

Where the holder is positioned to place the tooth at other than right angle relative to the platform 100, a flat rectangular brace plate 98 is welded to the holder 76 and to the platform surface 102 as shown in FIG. 2. In this manner, the angular disposition of the holder body 76 can be permanently fixed. Preferably, the plate 98 is arranged generally diagonally, at an acute angle relative to the platform 102 and in a direction extending parallel to both holder 76 and the platform edges so as to perform its bracing function.

The carrier is seated on the chain 18 by slipping the legs 108, 110 between the links 46 and 46 with the openings 1 12 aligned with openings 48. Bolt means 1 16 as shown then is passed through the aligned openings and fastened with suitable nuts so as to secure the tooth assembly by its carrier removably to the links. In contrast with the prior art, when the carrier is a part of the chain or at least permanently secured thereto, the tooth assembly 20 easily can be demounted when desired. The tooth 54 itself can be disassembled from its carrier utilizing an appropriately forked bar or prying member (not shown) having arms capable of being passed under the lugs 64 and 64. The length of such arms of the prying member is sufficient so that when the bar is lifted with the forks engaging beneath the upsets 64 and 64', free ends of the arms bear against the body 76 to enable the tooth to be dislodged from its position, pivoting so as to release its engagement with the plug 94. The rounded corner 74 serves as a cam surface to facilitate removal of the tooth 54 and its shank 60 from the holder body 76.

It should be pointed out that while other hard surfacing materials may be utilized in forming the formation 86, the preferred embodiment has its formation 86 formed of the RAYNITE product manufactured by the Rankin Manufacturing Co. of 6 1 6 South Marengo Avenue, Alhambra, Calif. This particular material is sold as a coated AC/CD electrode having a composition of 3.8% Chromium, 3.05% Carbon, 0.065% Titanium and 93.085% Iron. The material produces a Rockwell C hardness of 44-50.

What it is desired to secure by Letters Patent of the United States is:

l. A trenching apparatus comprising an orbital endless chain, a plurality of trencher tooth assemblies mounted to the chain at spaced intervals therealong for movement therewith, adjacent teeth being orientated at different angles relative to the direction of travel of said chain, each tooth assembly comprising, a tooth member having a depending shank, a multi-faceted tooth holder, slot means formed in the tooth holder and opening to one facet thereof for receiving said depending shank, a Pi shaped carrier, said tooth holder having multiple other angularly related facets, each of said other angularly related facets being selectively positionable on the carrier for permanent attachment thereto, the selection of said other facet fixing the angular disposition of the tooth holder on the carrier and determining the angle of orientation of the tooth relative to the direction of the travel of the chain, the selected said other facet being permanently secured to the carrier, means securing said shank within said slot means and means removably coupling said carrier to said chain, said tooth holder having a leading face and a ring-like formation formed on said face about the periphery thereof and defining, with said face, a cup-like configuration.

2. The apparatus as claimed in claim 1 in which said tooth holder is welded to said carrier.

3. The apparatus as claimed in claim 1 in which said chain has connecting links, and said carrier comprises a planar platform and a pair of depending spaced parallel depending legs, and said securing means comprises passage means formed in said legs and bolt means capable of being engaged through said passage means to engage one of said links.

4. The apparatus as claimed in claim 1 and brace means permanently secured to said holder and carrier maintaining and positioning of said holder relative to said carrier.

5. The apparatus as claimed in claim 1 in which said securing means comprise a pin and transverse passage formed in the tooth holder, a portion of which intercepts said slot means and plug means seatable within said transverse passage, said shank having an arcuate notch located for alignment with that portion of said transverse passage intersecting said slot means when said shank is installed within said slot means.

6. The apparatus as claimed in claim 5 in which said notch is arcuate and said tooth is capable of being displaced from said plug means to facilitate selective removal of said tooth from said slot means.

7. The apparatus as claimed in claim 1 in which the tooth has a substantially concave leading face.

8. The apparatus as claimed in claim 1 in which a pair of oppositely outwardly directed upsets are formed on said tooth at a location adjacent the mouth of the slot means when the shank is installed therein, said tooth being rotatable about said plug means to release said shank from said slot means on application of prying force to said upsets.

9. The apparatus of claim 1 in which said ring-like formation is irregular and formed of a hard surfacing material welded to the leading face of the holder.

10. A trencher tooth for use with a trench digging apparatus of the. type which includes an orbital linked endless chain having a plurality of trencher teeth arranged thereon at spaced intervals along the length thereof with adjacent teeth oriented outwardly at difinto one side portion of said holder, carrier means having the cross-sectional configuration of the Greek letter Pi defined by a platform and a pair of parallel depending legs, means for permanently securing said holder to.

said platform with said holder resting upon another side I portion of the holder, the selection of said last mentioned side portion determinative of the angular disposition thereby to define the aforesaid angle of orienta tion of said tooth body portion relative to the direction or movement of said chain, coupling means releasably securing said carrier to said chain, a ring-like formation of hard surfacing material on the leadingface of said holder, and angularly arranged brace means permanently secured to said holder and to said platform generally parallel to the opposite sides of the platform whereby to maintain the selected angular disposition of the holder upon said platform, said brace means comprising a flat metal plate weldably secured'to one side of said holder and to said platform.

11. The trencher tooth as claimed in claim. 10 in which said releaseable seating means comprise slot means formed in said holder opening to one side portion capable of receiving said shank telescopically fully therein with the tooth body oriented normally of said side portion, transverse passage means formed in said holder substantially normal to said slot means with a portion thereof intersecting said slot means, and plug means seatable within said transverse passage means to retain the shank within said slot means.

12. The trencher tooth as claimed in claim 10 in which there is angularly arranged brace means permanently secured to said holder and to said platform generally parallel to the opposite sides of the platform. whereby to maintain the selected angular disposition of the holder upon said platform.

13. The trencher tooth is claimed in claim 10 in which said ring-like formation has an irregular topographical configuration.

14. A trencher tooth for use with a trench digging ap paratus of the type which includes an orbital linked endless chain having a plurality of trencher teeth arranged thereon at spaced intervals along the length thereof with adjacent teeth orientated outwardly at different angles relative to the direction of movement of said chain, said trencher tooth comprising, a tooth member having a body portion, a cutting tip on said body portion and a depending shank portion; a substantially solid tooth holder of polygonal cross-section having plural side portions and a leading face at one end thereof, means releasably seating said shank portion into one side portion of said holder, carrier means having the cross-sectional configuration of the Greek letter Pi defined by a platform and a pair'of parallel depending legs, means for permanently securing said holder to said platform with said holder resting upon another side portion of the holder, the selection of said last mentioned side portion determinative of the angular disposition thereby to define the aforesaid angle of orientation of said tooth body portion relative to the direction or movement of said chain, coupling means releasably securing said carrier to said chain, a ring-like formation of hard surfacing material on the leading face of said holder, and angularly arranged brace means permanently secured to saidholder and to said platform generally parallel to the opposite sides of the platform whereby to maintain the selected angular disposition of the holder upon said platform, said brace means comprising a flat metal plate weldably secured to one side of said holder and to said platform.

15. A trenching apparatus comprising an orbital endless chain, a plurality of trencher tooth assemblies mounted to the chain at spaced intervals therealong for movement therewith, adjacent teeth being orientated at different angles relative to the direction of travel of said chain, each tooth assembly comprising, a tooth member having a depending shank, a multi-faceted tooth holder, slot means formed in the tooth holder and opening to one facet thereof for receiving said depending shank, a Pi shaped carrier, said tooth holder having multiple other angularly related facets, each of said other angularly related facets being selectively posisecuring said shank within said slot means and means removably coupling said carrier to said chain.

16. The apparatus as claimed in claim 15 in which the tooth has a substantially concave leading face. 

1. A trenching apparatus comprising an orbital endless chain, a plurality of trencher tooth assemblies mounted to the chain at spaced intervals therealong for movement therewith, adjacent teeth being orientated at different angles relative to the direction of travel of said chain, each tooth assembly comprising, a tooth member having a depending shank, a multifaceted tooth holder, slot means formed in the tooth holder and opening to one facet thereof for receiving said depending shank, a Pi shaped carrier, said tooth holder having multiple other angularly related facets, each of said other angularly related facets being selectively positionable on the carrier for permanent attachment thereto, the selection of said other facet fixing the angular disposition of the tooth holder on the carrier and determining the angle of orientation of the tooth relative to the direction of the travel of the chain, the selected said other facet being permanently secured to the carrier, means securing said shank within said slot means and means removably coupling said carrier to said chain, said tooth holder having a leading face and a ring-like formation formed on said face about the periphery thereof and defining, with said face, a cup-like configuration.
 2. The apparatus as claimed in claim 1 in which said tooth holder is welded to said carrier.
 3. The apparatus as claimed in claim 1 in which said chain has connecting links, and said carrier comprises a planar platform and a pair of depending spaced parallel depending legs, and said securinG means comprises passage means formed in said legs and bolt means capable of being engaged through said passage means to engage one of said links.
 4. The apparatus as claimed in claim 1 and brace means permanently secured to said holder and carrier maintaining and positioning of said holder relative to said carrier.
 5. The apparatus as claimed in claim 1 in which said securing means comprise a pin and transverse passage formed in the tooth holder, a portion of which intercepts said slot means and plug means seatable within said transverse passage, said shank having an arcuate notch located for alignment with that portion of said transverse passage intersecting said slot means when said shank is installed within said slot means.
 6. The apparatus as claimed in claim 5 in which said notch is arcuate and said tooth is capable of being displaced from said plug means to facilitate selective removal of said tooth from said slot means.
 7. The apparatus as claimed in claim 1 in which the tooth has a substantially concave leading face.
 8. The apparatus as claimed in claim 1 in which a pair of oppositely outwardly directed upsets are formed on said tooth at a location adjacent the mouth of the slot means when the shank is installed therein, said tooth being rotatable about said plug means to release said shank from said slot means on application of prying force to said upsets.
 9. The apparatus of claim 1 in which said ring-like formation is irregular and formed of a hard surfacing material welded to the leading face of the holder.
 10. A trencher tooth for use with a trench digging apparatus of the type which includes an orbital linked endless chain having a plurality of trencher teeth arranged thereon at spaced intervals along the length thereof with adjacent teeth oriented outwardly at different angles relative to the direction of movement of said chain, said trencher tooth comprising, a tooth member having a body portion, a cutting tip on said body portion and a depending shank portion; a substantially solid tooth body portion, a cutting tip on said body portion and a depending shank portion; a substantially solid tooth holder of polygonal cross-section having plural side portions and a leading face at one end thereof, means releasably seating said shank portion into one side portion of said holder, carrier means having the cross-sectional configuration of the Greek letter Pi defined by a platform and a pair of parallel depending legs, means for permanently securing said holder to said platform with said holder resting upon another side portion of the holder, the selection of said last mentioned side portion determinative of the angular disposition thereby to define the aforesaid angle of orientation of said tooth body portion relative to the direction or movement of said chain, coupling means releasably securing said carrier to said chain, a ring-like formation of hard surfacing material on the leading face of said holder, and angularly arranged brace means permanently secured to said holder and to said platform generally parallel to the opposite sides of the platform whereby to maintain the selected angular disposition of the holder upon said platform, said brace means comprising a flat metal plate weldably secured to one side of said holder and to said platform.
 11. The trencher tooth as claimed in claim 10 in which said releaseable seating means comprise slot means formed in said holder opening to one side portion capable of receiving said shank telescopically fully therein with the tooth body oriented normally of said side portion, transverse passage means formed in said holder substantially normal to said slot means with a portion thereof intersecting said slot means, and plug means seatable within said transverse passage means to retain the shank within said slot means.
 12. The trencher tooth as claimed in claim 10 in which there is angularly arranged brace means permanently secured to said holder and to said platform generally parallel tO the opposite sides of the platform whereby to maintain the selected angular disposition of the holder upon said platform.
 13. The trencher tooth is claimed in claim 10 in which said ring-like formation has an irregular topographical configuration.
 14. A trencher tooth for use with a trench digging apparatus of the type which includes an orbital linked endless chain having a plurality of trencher teeth arranged thereon at spaced intervals along the length thereof with adjacent teeth orientated outwardly at different angles relative to the direction of movement of said chain, said trencher tooth comprising, a tooth member having a body portion, a cutting tip on said body portion and a depending shank portion; a substantially solid tooth holder of polygonal cross-section having plural side portions and a leading face at one end thereof, means releasably seating said shank portion into one side portion of said holder, carrier means having the cross-sectional configuration of the Greek letter Pi defined by a platform and a pair of parallel depending legs, means for permanently securing said holder to said platform with said holder resting upon another side portion of the holder, the selection of said last mentioned side portion determinative of the angular disposition thereby to define the aforesaid angle of orientation of said tooth body portion relative to the direction or movement of said chain, coupling means releasably securing said carrier to said chain, a ring-like formation of hard surfacing material on the leading face of said holder, and angularly arranged brace means permanently secured to said holder and to said platform generally parallel to the opposite sides of the platform whereby to maintain the selected angular disposition of the holder upon said platform, said brace means comprising a flat metal plate weldably secured to one side of said holder and to said platform.
 15. A trenching apparatus comprising an orbital endless chain, a plurality of trencher tooth assemblies mounted to the chain at spaced intervals therealong for movement therewith, adjacent teeth being orientated at different angles relative to the direction of travel of said chain, each tooth assembly comprising, a tooth member having a depending shank, a multi-faceted tooth holder, slot means formed in the tooth holder and opening to one facet thereof for receiving said depending shank, a Pi shaped carrier, said tooth holder having multiple other angularly related facets, each of said other angularly related facets being selectively positionable on the carrier for permanent attachment thereto, the selection of said other facet fixing the angular disposition of the tooth holder on the carrier and determining the angle of orientation of the tooth relative to the direction of the travel of the chain, the selected said other facet being welded directly to the carrier, brace means extending between and permanently secured to the holder and carrier to further maintain the position of the holder relative to the carrier, means securing said shank within said slot means and means removably coupling said carrier to said chain.
 16. The apparatus as claimed in claim 15 in which the tooth has a substantially concave leading face. 